The invention relates to an absorption material, a method for the manufacture thereof, and its use as an absorbent for water, water vapor, aqueous solutions, aqueous or serous body fluids such as urine or blood, and for the absorption, retention and subsequent controlled release of water, aqueous solutions and/or the components dissolved therein, to other bodies.
In recent years a number of different polymers have been developed which have a high capacity for the absorption of water and body fluids. The majority of the products are manufactured on a starch basis, such as for example starch acrylonitrile graft polymers (U.S. Pat. Nos. 3,997,484, 3,661,815, 4,155,888 and 3,935,099), gelatinized starch derivatives (DE OS No. 2,702,781), starch acrylamide acrylamidopropanesulfonic acid graft polymer (U.S. patent application Ser. No. 955,827, filed 10-30-1978) or on a cellulose basis, such as derivatives of alkyl or hydroxyalkyl cellulose (JA Pat. No. 11/125,481), carboxymethylcellulose (BE Pat. No. 862,130, GB Pat. No. 1,159,949), and on a polysaccharide basis (DE OS No. 2,650,377). The all-synthetic absorbents described in numerous patents include crosslinked polymers and copolymers on an acrylic or methacrylic acid basis (DE OS No. 2,429,236, DE OS No. 2,614,662, U.S. Pat. Nos. 4,018,951, 3,926,891, 4,066,583 and 4,062,817, DE OS No. 2,712,043, DE OS No. 2,653,135, DE OS No. 2,813,635), or maleic acid derivatives (U.S. Pat. No. 4,041,228).
All these products are virtually insoluble in water and absorb a multiple of their weight in water, urine or other aqueous solutions.
Since these products are in a powder-like form, their incorporation into the end products (e.g., diapers, bandages etc.) is difficult and requires complex and expensive proportioning apparatus and applicators. It is especially difficult to handle a finely ground product of a grain size under 100 micrometers. The powder product adheres but poorly to the support, so that as a rule an adhesive must be used, and part of the absorption capacity of the powdered product is lost on that account.
Processes are also known for the preparation of absorbent fiber mixtures, in which a polymeric hydrophilic component, such as polyacrylic acid, carboxymethylcellulose etc., is admixed with the spinning solution, so that fibers of increased absorbency develop, as can be seen in German OS Nos. 2,550,345, 2,750,622, 2,750,900, 2,751,833, 2,905,424 and 3,036,415, and German Pat. No. 2,634,995. The hydrophilic component must be completely soluble in water and in the spinning solution. Since the weight ratio of the hydrophilic polymer component to the fiber component in these fiber mixtures is always less than 1, this also greatly limits the absorbency. In accordance with published European patent application No. 0023561, an improved absorbency is achieved in cellulose fibers by converting them in an inert medium to partially crosslinked, anoxidized carboxyalkylcellulose. Published European Application No. 0009322 describes the preparation of an absorbent paper from mixtures of cellulose fibers with insoluble fibers of amine-formaldehyde resin, in which a certain "freeness" (=degree of grinding) condition must be maintained.
On account of the great ability of polymeric absorbents to absorb water, it is quite difficult to incorporate these substances into the finished product out of an aqueous suspension, as in the case of paper manufacture. Either fiber suspensions of very low solid content (less than 0.1%, cf. DE OS No. 3,037,507) must be used in preparing the absorbent material, or the incorporation of the absorbent into the finished product can be accomplished (but only in the case of a carboxyl-containing absorbent) in two phases: first the absorbent is suspended in water in its acid form together with the fiber components, the paper web is formed on a paper machine and dried; the paper web is then neutralized in another step in order to achieve the desired absorbency of the finished product. The maximum ratio of the polymer component to the fiber component in the suspension is given as 65:35 by weight (DE OS No. 3,040,965).
Therefore an absorbent material would be desirable which would be very simple to make but would have a very high absorption capacity. Particularly desirable would be an absorption material in which the absorbent is anchored or fixed very firmly on or in the support, without any additional adhesives. Quite particularly advantageous would be an absorption material in flat form, such as a woven or nonwoven fabric, the absorbent being fixed in or on the flat support material. Such an absorption material ought to contain a very large amount of absorbent.
Setting out from known absorption materials consisting of a polymeric absorbent and a support, it is therefore the object of the invention to improve such an absorption material and avoid its disadvantages, especially to create an absorption material in which the absorbent is fixed permanently in or on the support without additional adhesives.